In data transmission networks, it is often necessary to protect stored and transmitted data from compromise or interception by unauthorized parties or eavesdroppers. Cryptography offers the protection necessary for data privacy. However, as the required amount of privacy increases, the transmission rate for encrypted data messages decreases because of an increased complexity of decryption.
One presently popular type of cryptographic system exhibiting this conflict between the competing interests of privacy and data transmission rate is the public key cryptographic system, especially one incorporating a trapdoor knapsack cipher. See U.S. Pat. No. 4,218,582 issued to M. Hellman et al. on Aug. 19, 1980.
Public key cryptographic systems afford authorized users a private means of communication even though unauthorized parties may intercept all of the communication. Heretofore, data transmission rates for these public key cryptographic systems have been constrained to be less than several kilobits per second because of decryption complexity. As such, public key cryptography is attractive only for low rate data and encoded voice transmission.